Airworthiness Directives; The Boeing Company Airplanes

We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 787-8 airplanes. This proposed AD was prompted by reports of hydraulic contamination of the power control unit (PCU) electro-hydraulic servo valves (EHSVs) used in the flight control system; this contamination caused a restriction in the EHSVs resulting in the display of status messages from the engine indication and crew alerting system (EICAS). This proposed AD would require installing markers to limit the hydraulic system fluid used to a specific brand, doing hydraulic fluid tests of the hydraulic systems, replacing hydraulic system fluid if necessary, and doing all applicable related investigative and corrective actions. We are proposing this AD to prevent the failure of flight control hydraulic PCUs, which could lead to reduced controllability of the airplane.